Eclipse控制台使用println()输出时部分字符不显示问题求助

Hey there, let's break down this odd issue you're having where characters seem to go missing after appending spaces with StringBuffer. It's definitely confusing, so let's walk through the most likely causes and how to debug them.

First, Verify the filler() Method #

This is the most probable culprit. If your filler() function isn't actually generating exactly 800 spaces each time you call it, that would immediately cause "missing" characters. Common mistakes here include:

• A wrong loop condition (like i < length - 1 instead of i < length)
• Accidental truncation logic inside the method

Test this in isolation to confirm:

// Add this to your main method to validate filler
System.out.println("Filler output length: " + filler(800).length());

If the output isn't 800, fix the filler() method to ensure it builds a string of the exact length you need.

Check if Characters Are Missing, or Just Not Showing #

Sometimes the issue isn't lost characters—it's your console hiding them. Many terminals and IDE consoles collapse consecutive spaces into one for display, even though the full string exists.

To confirm this:

1. Print the total length of your StringBuffer after all appends:

   System.out.println("Total string length: " + sb.length());
   

   Your expected length is 7 (from "000.00 ") + 5 * 800 = 4007. If the output matches this, the spaces are all there—your console just isn't displaying them properly.
2. For extra confirmation, iterate through the character array to verify spaces exist:

   char[] chars = sb.toString().toCharArray();
   // Check a section where spaces should be
   for (int i = 7; i < 20; i++) {
       System.out.println("Char at index " + i + ": '" + chars[i] + "' (ASCII: " + (int)chars[i] + ")");
   }
   

   You should see ASCII 32 (the code for space) for each of these positions.

Rule Out Other Edge Cases #

• Unintended StringBuffer modifications: Double-check if you accidentally called methods like delete(), setLength(), or replace() before printing—these could truncate your string.
• JDK edge cases: While extremely rare, try switching to StringBuilder (since you're using this in a single-threaded main method, you don't need StringBuffer's thread safety) to rule out any obscure thread-related bugs.

Example of a Broken Filler Method #

Just to make this concrete, here's a common mistake that would cause missing spaces:

// This version generates only 799 spaces instead of 800
private static String filler(int length) {
    StringBuilder sb = new StringBuilder(length);
    for (int i = 0; i < length - 1; i++) { // Wrong loop condition!
        sb.append(' ');
    }
    return sb.toString();
}

Fixing the loop to i < length would resolve the missing characters here.

内容的提问来源于stack exchange，提问作者Alexandre Miziara